Transformer winding structure using corrugated spacers

ABSTRACT

Corrugated spacers are disposed between winding layers of a transformer winding to enable circulation of air between the layers. Elongated reinforcing rods are placed in corrugations at the corner regions of the winding and adjacent wedges between the winding and the transformer core. Dielectric sheaths of relatively high dielectric constant are disposed between the outermost and innermost winding layers while relatively low dielectric constant sheaths are placed between adjacent pairs of interior layers, thereby to equalize the distributed capacitance between adjacent layers. A dielectric barrier between the high and low voltage windings of a transformer consists of a sheath of dielectric layers wherein the inner and outermost layers have a higher dielectric constant than the interior layers.

United States atent Weber et al. 1 July 24, 1973 [54] TRANSFORMER WINDING STRUCTURE 3,386,058 5/1968 Michel 336/60 USING CORRUGATED SPACERS 3,464,043 8/1969 Benko et al 336/185 X [75] Inventors: Hans J. Weber, Cornwells Heights; FOREIGN PATENTS OR APPLICATIONS James R. Ruckel, King of Prussia, 1,278,093 10/1961 France 336/60 both of Pa. 240,559 1925 Great Britain 336/206 [73] Assignee: :h-iT-E Inliperial Corporation, Spring Rama), EJQ 91". om L Kozma ouse A ttorney-Sidney G. Faber, Samuel H. Weiner et al. [22] Filed: Mar. 24, 1972 21 Appl. No.: 237,639 [57] ABSTRACT Corrugated spacers are disposed between winding layers of a transformer winding to enable circulation of air [52] U.S. Cl 336/60, 336/185, 336/223 between the layers. Elongated reinforcing rods are [51] Int. Cl. H011 27/08 placed in corrugations at the comer regions of the [58] Fleld of Search...., 336/60, 206, 209, i i and adjacent wedges between the winding and 336/185 223 the transformer core. Dielectric sheaths of relatively high dielectric constant are disposed between the out- [56] References Cted ermost and innennost winding layers while relatively UNITED STATES PATENTS low dielectric constant sheaths are placed between ad- 3,386,060 5/1968 Reber 336/60 x j Pairs of interior layers, thereby to equalize the 3,431,524 3/ 1969 Brouerman 336/60 distributed capacitance between adjacent layers. A di- 3,237,136 2/1966 Ford 3361206 X electric barrier between the high and low voltage wind- 2,602,035 7/1952 camilli et al 336/209 X ings of a transformer consists of a sheath of dielectric f il f at layers wherein the inner and outermost layers have a 0 us on 2,,"0947 6/1955 Gaston I I I I I 336,60 higher dielectric constant than the interior layers. 3,252,l 17 5/1966 Fischer 336/60 X 8 Claims, 9 Drawing Figures fly 04 46 v7 a; 37 .;a 3,9 /02 I l f o l l l I I] II 25 44 4.; a2 6/ Y If I I z TRANSFORMER WINDING STRUCTURE USING CORRUGATED SPACERS RELATED APPLICATIONS This application is related to application Ser. No. 237,714 filedMar. 24, 1972 entitled Insulation Structure Transformer windings in the name of Hans J. Weber, and assigned to the assignee of the present invention, and which claims aspects of the dielectrics used in the transformer winding of the present application.

BACKGROUND OF TI-IE INVENTION This invention relates to a winding construction for air-cooled transfonners and more specifically relates to the use of corrugation spacers and corrugation reinforcement for the winding of an air-cooled, or dry-type transformer.

In order to efficiently cool transformer windings of an oil-filled transformer, it is known that corrugated sheets can be placed between adjacent windings to form channels between windings through which cooling oil can circulate. Generally, this oil circulates by convection force.

Corrugated spacers have not, heretofore, been used in connection with air-cooled transformers. Thus, it was found that these spacers defined too small an air channel to allow sufficient flow of air to produce effective cooling. That is, since oil has a relatively high thermal capacity, substantial heat can be removed from the winding with a relatively small volumetric oil flow past the winding. A much larger flow of air was necessary to remove the same amount of heat, but the corrugation excursion (of less than about one-fourth inch) prevented this necessary flow of air.

A second feature which prevented the direct adoption of oil transformer corrugation sheets in air-cooled transformers is that the air-cooled winding conventionally operates at a much higher temperature (up to 220C.) than the oil transformer. The corrugated sheets used in oil transformers are conventionally made of a bone fiber material which cannot sustain this high temperature.

BRIEF SUMMARY OF THE INVENTION The present invention is based on the recognition that corrugated spacers can be applied to air-cooled transformers by enlarging the excursion of the corrugations to allow increased size air channels with novel reinforcing means to prevent collapse of the corrugations at high stress points, and by using high temperature materials for the corrugation board. Thus, a corrugation with an excursion in excess of about three-eighths inch is used, with insulation rods disposed in those corrugations which would otherwise be collapsed by high stresses, such as appear at the corners of the winding and adjacent the wedges which secure the windings on the transformer core. The material selected for the corrugations is a high temperature material, capable of being set in a corrugated form. Typically, moldable materials may be used, which can easily withstand temperatures of 220C. and maintain high strength at these temperatures. In order to prevent collapse of the relatively large corrugations at high stress regions, elongated insulation rods are secured in the corrugations at the comers of the winding, and adjacent wedges used to hold the winding on the core.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates a three-phase transfonner which has three windings, which could be constructed in accordance with the present invention.

FIG. 2 schematically illustrates one high voltage winding of the transformer of FIG. 1.

FIG. 3a is an end elevational view of one end of a transformer such as the one of FIG. I which incorporates a coil having a construction which uses the present invention.

FIG. 3b is a partial side elevational view of FIG. 30.

FIG. 4 is a cross-sectional view of FIG. 3a and is taken across section line 4-4 in FIG. 30.

FIG. 5 is an enlarged view of a portion of FIG. 4 to illustrate the construction of the corrugation spacer.

FIG. 6 is an enlarged view, in perspective, of a portion of the high-voltage to low-voltage barrier shown in FIG. 4.

, FIG. 7 is an enlarged view of a winding corner of FIG. 4 to illustrate the placement of rods and wedges in the winding support structure.

FIG. 8 schematically represents the distributed capacitances affecting the distribution of impulse voltage across the coil layers of a high voltage winding.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. I partly schematically illustrates a conventional transformer which may use the present invention in its winding structure. The transformer of FIG. 1 includes a magnetic core having three core legs 10, II and 12 joined by upper yoke 13 and lower yoke 14. The core may be made of conventional stacked laminations, and legs 10, 11 and 12 can be of any desired cross-section, which conventionally is generally rectangular. Each of core legs l0, l1 and 12 carry respective low voltage windings 20, 21 and 22 which are wound concentrically with outer high voltage windings 23, 24 and 25. The high and low voltage windings 20 to 25 may be arranged in any desired multiphase connection. The invention herein involves the specific construction ofa winding which may be used in the transformer of FIG.

1, when the winding may be air cooled. It is to be noted, however, that the invention herein may be used for any type electrical winding, which is used in any type electromagnetic device.

While any terminal construction could be used for the various windings, each winding is shown in FIG. 1 as having a simple pair of terminals. FIG. 2 schematically shows that winding 25, for example, may have a plurality of tap terminals 30 to 34, and a second terminal 35. FIG. 2 further schematically illustrates the winding 25 as constructed of a plurality of identical layers of windings 36 to 43, and an end layer 44 which contains the taps 30 to 34.The schematically shown wound layers 36 to 43 are wound over an insulation barrier 45 to be later described, and which insulate the high voltage and low voltage windings. Taps 30 to 34 may be made in any desired manner. By way of example, one suitable tap arrangement is shown in copending application, Ser. No. 167,174, filed July 29, 1971, in the name of Ruckel et al..

FIG. 3a is an end view of the transformer of FIG. I when adapted with a winding construction made in accordance with the present invention, while FIG. 3b is a side-elevational view of FIG. 3a and specifically shows one winding and the taps 30 to 34 of the winding (winding 25 of FIG. 1). The winding construction as seen in FIGS. 3a and 3b shows the external high voltage winding 25, and protruding above and below the high voltage winding 25 is the high voltage to low voltage barrier 36a. A low voltage winding, not shown in FIGS. 3a and 3b, is contained within the barrier 36a and is wound concentrically with winding 25 on the core leg 12 of the transformer. The winding structure of the invention is most clearly shown in cross-section in FIG. 4.

FIG. 4 illustrates the square configuration of core leg 12 where it will be understood that core leg 12 could also have other configurations, if desired. The core leg 12 has wrapped thereon a glass tape layer 50 to insure insulation integrity between the grounded core and the winding to be connected thereon. The full winding is wound on a winding machine separately from the core and, in the embodiment herein, consists of a low voltage winding contained within the interior of the overall winding structure and an outer high voltage winding. The low voltage winding shown in FIG. 4 has an interior, upwardly extending terminal 51 which extends beyond the upper end of the winding, and may consist of a conductive foil 52 wound around an axis to form nine turns, which terminate in terminal 53. Note that terminals 52 and 53 correspond to the pair of terminals shown for the low voltage winding 22 in FIG. 1. The height of the low voltage winding is generally shown in dotted lines in FIG. 3a, with the low voltage winding 22 being contained within the insulation barrier 36a. A suitable insulation layer will be used over the surface of the material used for the low voltage winding. By way of example, a layer of asbestos reinforced with glass may be used to insulate the low voltage winding.

The insulation barrier 36a is then wound around the exterior of the low voltage winding 22 where the insulation barrier 36a consists of a composite of high dielectric and low dielectric layers, most clearly shown in FIG. 6. Thus, in FIG. 6, the barrier 36a consists of two outer layers 60 and 61 of a relatively high dielectric constant material with, for example, fourteen interior layers 62 of a relatively low dielectric constant material. Good results have been obtained when using mica having a thickness of about 0.010 inch for the outer layers 60 and 61, and using a lower dielectric constant material, such as a material known as Nomex M, having a thickness of 0.01 inch for each of the 14 interior layers 62. Nomex M is a trademark of DuPont, and generally is a composite of nylon and mica.

By using materials of a relatively high dielectric constant in the area of high dielectric stress between the high and low voltage windings, the dielectric field lines distributed between layers 60 and 61 of FIG. 6 will be relatively spread apart thereby to decrease the dielectric gradient. Thus, it is possible to reduce the space between the high and low voltage windings, thereby saving material costs.

The high voltage winding 25 is then wound on top of the barrier 36a and consists of the nine layers 36 to 44, wherein the layers 36 to 42 may each contain fiftythree turns of aluminum wire which can, for example, have a crosssection of 0.115 by 0.375, which wire is appropriately insulated. Layer 43 may then have 49 turns, while the outer layer 44, which contains the taps 30 to 34,, may have 48 turns. It will be noted that a start terminal (terminal 35in FIG. 1) will come from the first layer 36, while the second terminal of the high voltage winding 25 in FIG. 1 could, for example, be the tap terminal 34 of FIG. 2.

In order to provide appropriate air cooling, whether forced air cooling, or natural convection cooling, each of the winding layers of both the high voltage and low voltage windings are spaced by insulation corrugated spacers. By way of example, corrugated spacers and 71 are typically shown, respectively, between the first and second, and second and third windings of the low voltage winding 22. These corrugated spacers are shown in more detail in FIG. 5, where it is seen that they have an undulating configuration which defines side-by-side air channels which extend along the full length of the winding layers. Preferably, the corrugations will have a total thickness or excursion of at least three-eighths inch in order to define sufficiently large area air channels to allow a copious flow of cooling air through the channels.

In addition, these corrugations are made of a material which is capable of withstanding the relatively high temperature rise of a dry-type or air-cooled transformer. Good results have been obtained with corrugations made of polyimid resins, such as Gemon-L, made by the General Electric Corporation. Other suitable materials are moldable materials, such as Glastic 200, made by the Glastic Corporation, or HST, made by the Haysite Corporation. The material thickness of these corrugations may be about one thirty-second inch to provide satisfactory mechanical strength over most of the area of the corrugations. It will be noted that these corrugations could be crushed at high stress levels of the winding, but this problem is solved through the use of novel reinforcing rods to be described hereinafter.

Corrugations similar to corrugations 70 and 71 are disposed between each of the winding layers of the low voltage winding, although if desired, corrugations be tween only selected pairs of layers could be used. In the preferred embodiment of the invention, however, and as shown in FIGS. 4 and 5, corrugation spacers are provided between each of the foil winding layers 72, 73 and 74, as well as the remaining foil layers. It should be specifically noted that the corrugation region is made on selected peripheral portions of the coil which are disposed externally of the planes defined by the sides of yokes l3 and 14. In this manner, a clear air passage from the bottom of the transformer to the top is defined without interference from the yokes of the transformer.

A similar arrangement of corrugation spacers of identical material to spacers 70 and 71 is provided for the high voltage winding. Thus, corrugation spacers such as spacers 75 and 76 are disposed between winding layers 36 and 37, and 37 and 38, respectively. Similar corrugation structures are provided between each of the other winding layers of the high voltage winding. It will be seen that the corrugation spacer used for the high voltage winding also define air channels on the outside of the yokes of the transformer, thereby to provide clear unrestricted air-flow channels through which cooling air may be carried.

In addition, and in the winding shown in FIG. 4, corrugation spacers 77 and 78 are formed in the region passing between the yokes 13 and 14 of the transformer, and between winding layers 38 and 39 to help conduct heat from this interior portion of the winding even though the cooling air path will be partly blocked by the yokes 13 and 14.

As pointed out previously, the corrugation structure is sufficiently strong to maintain its configuration and physical strength in most parts of the coil. However, in high stress regions, it is possible that the corrugation could be crushed. In order to prevent the local crushing of the corrugation, and as shown in FIG. 4, the corner regions at which the winding layers bend are reinforced by insulation rods disposed within the corrugation and adjacent the corner region. Typical insulation rods are shown as rods 80, 81, 82, 83 and 84, which are generally disposed at the last corrugation region of their respective corrugation spacers, and at the region where the winding layer turns a corner. The insulation rods will then support and prevent the corrugation from collapsing duringwinding and extend the full length of the on the core 12, the upper yoke member 13 is disassembled in standard fashion, and the total winding is mounted concentrically with the winding leg 12, and is secured in place on the winding leg 12 by appropriate mounting structures, which could include insulation wedge members, such as the wedge members 90 to 95 shown in FIG. 4. These insulation wedges are simply elongated sticks which may be slightly wedge-shaped and which are forced between the interior of the winding and the exterior of the core leg 12. It has been found useful to dispose reinforcing rods in the first corrugation 70 at regions adjacent these wedge members to prevent local collapse of the interior corrugation 70.

Thus, in FIG. 4 it is seen that insulation rods, for example, rods 96 and 97 are placed adjacent the wedges 91 and 92 to prevent local collapse of the corrugation 70 at'these regions.

A further important feature of the winding structure of FIG. 4 consists of the use of selective dielectric layers between thewinding layers forming the high voltage winding. Thus, as shown in FIG. 4, a dielectric sheath or layer of tape is formed between each of the winding layers. These dielectric sheaths consist,for example, of the sheaths 101 to 109.

Inaccordance with an important feature of the present invention, the inner and outermost sheaths 101 and 109 of the high voltage winding are made of a material having a dielectric constant which is higher than the dielectric constant of the interiordielectric sheaths 102 to 108. Thus, each of the winding layers 36 to 44 may be equally spaced, for example, by three-eighths inch, but the insulation sheaths 102 to 108 are formed of two layers of 0.010 inchthick Nomex M, while the exterior insulation layers 101 and 109 are formed of, for example, two layers of 0.0l inch thick mica. With this structure, materials of higher dielectric constant are disposed betweenthe first and last layers of the high voltage winding, thereby to increase the distributed capacitance of the first and last layers of the transformer winding in order to substantially equalize the capacitance between all layers in order to cause equal voltage distribution of an impulse voltage applied to the high voltage winding.

This construction can be better understood inconnection with FIG. 8, which schematically illustrates the high voltage winding '25 in connectionwith its distributed capacitances. Thus, there is an imaginary neutral plane shown by the dotted lines N between each pair of adjacent winding layers, with the distributed capacitance between winding layers being schematically illustrated as capacitances connected from the winding to the neutral plane. The total winding will be coupled to ground through the equivalent capacitances C and C,,. However, the equivalent layer capacitances of the first layer 36 to the second layer 37 and of the outer layer44 to the next innermost layer 43 will be a capacitance C which is smaller than the distributed capacitances C between the remaining interior adjacent layers 37 to 43. Consequently, an impulse voltage applied to the high voltage winding could, for example, due to the effect of a lightning stroke, not distribute equally between the winding layers,ibut rather a larger percentage of the voltage will appear between layers 36 and 37, and 43 and 44, than between the adjacent layers.

In accordance with the present invention, and by using higher dielectric constant material between the first and last pairs of layers, the equivalent capacitance between these layers is increased to a value approaching that of the distributed capacitance between the remaining interior layers, thereby toimprove the voltage distribution pattern across the winding due to impulse voltages. Note that this selection of different dielectric constant materials allows the transformer winding-construction to use identical interlayer spacing thereby simplifying the manufacture of the transformer. Clearly, other combinations of dielectric materials could have been selected, if desired.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, notby the specific disclosure herein, but only by the appended claims. I

The embodiments of the invention in which an exclusive privilegeor property is claimed are defined as follows:

1. An air-cooled electromagnetic device comprising,

in combination: g

an elongated magnetic core; a

an electrical winding means wound on said core and consisting of a plurality of concentric winding'layers connected in given circuit relation with respect to one another;

a plurality of corrugation members of insulation material, each defining a plurality of sideby-side air channels extending parallel to the direction of elongation of said core; saidplurality of corrugation members each having a height substantially equal to the height of said electrical winding means, and having a width which extends around only a portion of said electrical winding;

each of said corrugation members being disposed between selected adjacent winding layers of said plu-' rality of concentric winding layers to define air channels in contact with the opposing surfaces of each of said adjacent winding layers said corrugation memers having corrugation excursions of at least about three-eighths inch, and being formed of a material capable of maintaining its form and strength in working ambient temperatures of about 220C;

said core having a rectangular configuration; said corrugation members extending around at least one of the corners of said core; and elongated insulation rod members disposed in the air channels of said corrugation members in the region where said corrugation members are bent to conform to the said corner of said core.

2. The device of claim I wherein each pair of adjacent concentric winding layers has one of said corrugation members therebetween.

3. The device of claim 1 wherein said winding means includes a high voltage winding and a low voltage winding, each consisting of first and second pluralities of layers of said plurality of winding layers.

4. The device of claim 3 wherein each pair of adjacent concentric winding layers has one of said corrugation members therebetween.

5. The device of claim 1 which further includes a plurality of parallel, elongated wedge members fitted between the interior surface of said electrical winding means and the adjacent surface of said core; said elongated parallel wedge members disposed parallel to said side-by-side air channels in said corrugation members.

6. The device of claim 5 which further includes elongated insulation rods disposed in the air channels defined by the innermost of said corrugation members which are adjacent to said wedge members.

7. The device of claim 1 which further includes top and bottom parallel yokes disposed at the opposite ends of said magnetic core; the opposite sides of said top and bottom yokes and said elongated core disposed in spaced parallel planes; said electrical winding means having portions thereof extending beyond the said spaced parallel planes; said corrugation members being at least partially disposed in said extending portions, whereby said air channels defined by said corrugation members are uninterrupted by said yokes.

8. The device of claim 1 wherein said corrugation member is formed, at least in part, of an epoxy resin. k 

2. The device of claim 1 wherein each pair of adjacent concentric winding layers has one of said corrugation members therebetween.
 3. The device of claim 1 wherein said winding means includes a high voltage winding and a low voltage winding, each consisting of first and second pluralities of layers of said plurality of winding layers.
 4. The device of claim 3 wherein each pair of adjacent concentric winding layers has one of said corrugation members therebetween.
 5. The device of claim 1 which further includes a plurality of parallel, elongated wedge members fitted between the interior surface of said electrical winding means and the adjacent surface of said core; said elongated parallel wedge members disposed parallel to said side-by-side air channels in said corrugation members.
 6. The device of claim 5 which further includes elongated insulation rods disposed in the air channels defined by the innermost of said corrugation members which are adjacent to said wedge members.
 7. The device of claim 1 which further includes top and bottom parallel yokes disposed at the opposite ends of said magnetic core; the opposite sides of said top and bottom yokes and said elongated core disposed in spaced parallel planes; said electrical winding means having portions thereof extending beyond the said spaced parallel planes; said corrugation memBers being at least partially disposed in said extending portions, whereby said air channels defined by said corrugation members are uninterrupted by said yokes.
 8. The device of claim 1 wherein said corrugation member is formed, at least in part, of an epoxy resin. 